Add items to an existing list mvc5 - list

Question

(I am a new developer)I have a list that I put in a viewBag to make a dropwdown in my view and I would like to add 3 elements to this list so that we can see them at the end of my dropdown. I make a timesheet for the employees and I have a dropdown of the projects that the person worked during the week and I would like to add at the end of the dropdown the 3 options "Vacancy", "Unplanned Absence", "Planned Absence" if the person has been on leave instead of working.
This is my request for the projects :
var projectAssignment = (from pa in db.ProjectAssignment
join p in db.Projects on pa.ProjectId equals p.ID
where pa.EmployeeId == EmployeeId && pa.StartDate !=null && (pa.EndDate == null || pa.EndDate >= DateTime.Now)
select new ProjectTimesheetList
{
ProjectName = p.ProjectName,
ProjectId = pa.ProjectId
});
ViewBag.ProjectTimeSHeet = projectAssignment;
This is a the modal to add my timehseet and i want to put the 3 daysoff type at the end of dropdown, so in this case after "NatureBooker"
And this is my code of my dropdown:
<select name="' + row + '_' + col + '" class="custom-select" id="tsCell_' + row + '_' + col + '" data-row="' + row + '" data-col="' + col + '">' +
'<option value="">----Select----</option>#Html.Raw(projsStr)</select>';
SOLUTION:
var projectAssignment = (from pa in db.ProjectAssignment
join p in db.Projects on pa.ProjectId equals p.ID
where pa.EmployeeId == EmployeeId && pa.StartDate !=null && (pa.EndDate == null || pa.EndDate >= DateTime.Now)
select new ProjectTimesheetList
{
ProjectName = p.ProjectName,
ProjectId = pa.ProjectId
});
List<ProjectTimesheetList> projectAssignments = projectAssignment.ToList();
projectAssignments.Add(new ProjectTimesheetList
{
ProjectName = "Vacancy",
ProjectId = -1,
});
projectAssignments.Add(new ProjectTimesheetList
{
ProjectName = "Unplanned Absence",
ProjectId = -2,
});
projectAssignments.Add(new ProjectTimesheetList
{
ProjectName = "Planned Absence",
ProjectId = -3,
});
ViewBag.ProjectTimeSHeet = projectAssignments;
And the result:

Answer 1

Still not clear what exactly you want, but if my guess is right you probably want to add "fake" projects to the enumerable you're binding to (not a list, by the way).
As long as you understand that this is absolutely wrong and grounds for being fired on the spot, here you go:
ViewBag.ProjectTimeSHeet = projectAssignment
.Concat(new[]
{
new ProjectTimesheetList
{
ProjectName = "Vacancy",
ProjectId = -1,
},
new ProjectTimesheetList
{
ProjectName = "Unplanned Absence",
ProjectId = -2,
},
new ProjectTimesheetList
{
ProjectName = "Planned Absence",
ProjectId = -3,
},
});

Answer 2

var myOptions = {
val1 : 'Vacancy',
val2 : 'Unplanned Absence',
val3 : 'Planned Absence',
};
var mySelect = $('#dropdownID');
$.each(myOptions, function(val, text) {
mySelect.append(
$('<option></option>').val(val).html(text)
);
});
through Javascript
var ddl = document.getElementById("dropdownID");
for ( let key in myOptions )
{
var option = document.createElement("OPTION");
option.innerHTML = key
option.value = myOptions[key]
ddl.options.add(option);
}